Re: [LARTC] When the inside functions of a sfq are called ?

[Andy Furniss <andy.furniss@dsl.pipex.com>]

Adrian Saileanu wrote:
>>Adrian Saileanu wrote:
>>
>>>  I read the sched/qdiscs code from kernel source ... and I have some
>>>questions :
>>>
>>>  When the .enqueue, .dequeue, .drop, .requeue functions are called ?
>>
>>Do you mean in sfq.c - ie sfq_enqueue etc. Maybe you mean something else.
> 
> 
> Yes, I ment the functions in the Qdisc_ops struct :
> 
> +static struct Qdisc_ops dup_qdisc_ops = {
> +        .next                = NULL,
> +        .cl_ops                = NULL,
> +        .id                = "sfq",
> +        .priv_size        = sizeof(struct sfq_sched_data),
> +        .enqueue        = sfq_enqueue,
> +        .dequeue        = sfq_dequeue,
> +        .requeue        = sfq_requeue,
> +        .drop                = sfq_drop,
> +        .init                = sfq_init,
> +        .reset                = sfq_reset,
> +        .destroy        = NULL,
> +        .change                = sfq_init,
> +        .dump                = sfq_dump,
> +        .owner                = THIS_MODULE,
> +};
> 
> 
> 
>>  What
>>
>>>is the event that triggers them and how often this event apears ( per
>>>second ? ) ?
>>
>>I don't know as such, but always assumed that when attached to HTB  - a
>>packet gets enqueued if there aren't enough (c)tokens to send it and
>>dequeued when there are. As for timing I don't think sfq uses any - it's
>>up to whatever it is attached to.
>>
> 
> 
>   Ok, the packet gets enqueued ... and the queue gets full. Then if a new
> packet arrives and the queue is still full (  it has not been dequeued )
> then this packet is dropped. 

I think a packet gets enqueued - then the queue length is checked and if 
it's full sfq_drop is called. sfq_drop drops a packet from the longest 
slot - hence the packet that filled the queue may or may not be the one 
that is dropped depending on which slot it got hashed to.

> My question is ... is the queue dequeued
> when it is full ? Or t can be dequeued even when the maximum has not
> been reatched ? When this .dequeue function is called ?

It is normal for dequeue to be called before the queue is full - exactly 
when it gets called is the job of whatever the sfq got attached to.

Andy.

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